Mental bloviations on the world as seen through the eyes of a pathological neuroscientist.

Saturday, October 29, 2011

Zombie Brain: Flesh Addiction

This is yet another installment of multi-day series on The Zombie Brain. Be sure to visit Oscillatory Thoughts tomorrow for another post in this series!

Symptom 8: Flesh addiction

“Braainss... BRAAAINS!” Zombies call out for them like a man calls out for water after a week in the desert. Yet no matter how much they eat, they can never be satisfied. It’s as if the craving to consume brains and/or human flesh is the sole thought running through a zombie’s “mind”. Zombies will even risk loss of “life” and limb to satisfy these urges.These symptoms mirror those seen in dysfunction of the “reward circuits” in the brain. It’s as if the living dead are addicted to flesh and flesh consumption is a compulsion.

The sense of reward, or the “high”, that you experience originates first from dopamine cells that rest in an area of the brain collectively known as the ventral striatal reward pathway. This includes a larger network of areas in the neocortex, midbrain and brainstem.

In many ways this circuit starts and ends in the brainstem with the release of dopamine. Note that these are a different set of dopamine neurons than those involved in the aggression circuit we discussed earlier. Activating these “reward cells” with stimulation (e.g., drugs, food, sex, etc., in humans, or direct electric stimulation in animals) causes them to transmit dopamine to other regions in the cortex and subcortex such as the striatum. This reinforces the drive for future reward seeking behaviors.

These signals converge to a set of cells in the nucleus accumbens, which is essential for determining the motivational significance of the reward stimulus, causing the person to think, “Mmmmm that was fun; I’ll do that again.”

In cases of extreme drug abuse, simply showing pictures of drugs to an addict will engage this reward circuit. The same is true for people addicted to eating: showing them pictures of food can reengage the same reward regions as eating.In zombies, this dopamine reward circuit is likely in overdrive. Paired with a loss of the feeding “off-switch” in the brain, this could lead to the insatiable appetite that zombies have. Of course, in humans fatty diets cause more hunger and the brain is a highly fatty substance, so unfortunately, the more the zombie eats... the more it wants… But we'll discuss that a bit later.We expect that if you put a zombie in an MRI machine and showed it pictures of human flesh, you would detect activation in many regions of this ventral reward circuit. In fact, these would be the same activation patterns we'd expect to see in the brain of a (living) drug addict when presented with pictures of their drug of choice.

What fMRI would look like in the zombie brain.

But why isn’t a zombie satisfied even after it has consumed an entire human on its own? Well that's a whole other blog post. Let's just say the zombie brain doesn't know or doesn't care when it's full.

So today's lesson shows us that zombies are depraved flesh addicts who will stop at nothing to get their next fix (i.e., you).

As a program official at NIDA, I found this a "scream" to read, as I dole out candy to the little neighborhood urchins. I'm wondering though, if you couldn't boost the fMRI contrast using fleshy odors, instead of just images. A contrast between post-big-game Teenage cheerleader musk versus Ed Asner after climbing stairs- would send the zombie accumbens into meltdown!

You could do a double dissociation between the responses to "Teen Spirit" body wash versus the smell of decaying flesh in zombies versus humans. Of course Ed Asner sweat would be the control condition... no one necessarily LIKES that smell, but even zombies can get mad at Ed Asner.